1. Field of Invention
The present invention relates to automotive interior trim articles containing a panel-like structure mountable in an automobile vehicle to form a part of the interior thereof, and in particular to automobile interior trim articles, such as instrument panels and door panels, which conceal a secondary restraint system including an air bag. The present invention further relates to a process for making the aforementioned automotive interior trim articles.
2. Description of Related Art
The escalation of the commercial significance of air bag restraint systems in automobiles as secondary restraint systems has manifested itself in the appearance of air bag restraint systems in many, if not most, new automobiles. The commercial impact of such secondary systems is attributable both to government regulations and consumer demand for safety.
Generally, air bag restraint systems are concealed from view during normal operation of the vehicle by arranging the air bag restraint systems behind automotive interior trim articles, such as instrument panels and/or door panels.
In order to permit the deployment of the air bags upon collision of the vehicle, interior trim articles are often formed with a multi-layered structure comprising a rigid substrate having hidden doors formed therein, an outer decorative skin layer, and a soft cellular polyurethane foam layer formed therebetween. The hidden doors of the rigid substrate are configured and arranged in such a manner that the edges of the doors define discernible patterns, such as patterns in the form of H, C, U, and X shapes.
During deployment of the air bag, the air bag is actuated via a gas generating system and expands from a folded inoperative state to a fully inflated state. The expansion of the gas inflates the air bag against the backside of the hidden doors and forces the hidden doors to open into the passengers' compartment of the vehicle. The emergence of the hidden doors into the passengers' compartment creates a passageway which permits deployment of the air bag into the passengers' compartment of the vehicle and thereby protects the passengers from violent collision against the panel-like structure.
In order to minimize obstruction of the passageway through which the expanding air bag traverses, the underside of the outer skin of the multi-layered structure can be provided with structurally weakened tear seams. These tear seams often take the form of perforated or channel-like patterns, and are constructed and arranged to substantially correspond to and overlay the pattern (e.g., H-shaped) defined by the hidden doors of the rigid substrate. During deployment of the air bag, the outer skin tears or fractures along the structurally weakened tear seams. Absent the presence of such structurally weakened tear seams in the outer skin, the outer skin may possess sufficient internal strength to refrain from fracture upon deployment of the rapidly expanding air bag. If the skin does not fracture, the entire outer skin can become separated from the rigid substrate and/or the multi-layered structure can be dismounted from the vehicle frame, thereby imperiling the safety of the passengers.
Different techniques have been proposed to form a multi-layered structure having an outer skin with a structurally weakened, rupturable tear seam. One conventional technique involves the preparation of a rotational-cast poly(vinyl chloride) ("PVC") skin by providing a powder box including a seam-defining structure or gasket, which partitions the powder box into two chambers. A PVC powder with appropriate colorants and additives, such as plasticizers, is retained in each of the chambers. Where a dual-tone appearance is desired, the chambers can be supplied with PVC powders containing different colorants, in which case the seam-defining structure simultaneously serves as a color division rim. The powder box is then engaged to a metal mold component to define a closed casting system having the seam-defining structure closely spaced from a heated mold surface of the metal mold component. The PVC powder is then tumbled against a heated molding surface of the metal mold by a rotational casting method until the PVC powder is formed against a moderately heated mold surface in a gelled state. Excess powder collects in the powder box, and is thereafter separated and removed from the mold. Since the seam-defining structure obstructs the gelling of PVC powder on the portion of the heated mold surface therebelow, the structurally weakened portion of the skin is formed below the seam-defining structure. A lower density or lower strength tear seam material (also referred to as a filler material) is then sprayed into the perforated or channel-like seams and gelled. The gelled PVC material and the gelled tear seam material are then fused by heating the materials to their fusion temperatures, and thereafter cooled to provide the PVC-based covering in a thermoplastic solid state. The skin can then be united with the rigid substrate, such that the low density material of the outer skin is positioned to substantially correspond to and overlay the edges of the hidden doors.
There are at least two problems associated with the above-described conventional method.
First, the presence of the seam-defining structure hinders the normal compacting of the PVC powder which occurs during rotation of the closed system. Hence, the portion of the skin layer corresponding to the structurally weakened tear seam possesses a greater porosity than the remainder of the skin. The difference in porosity between the structurally weakened portion and the remaining portion of the outer skin makes the pattern of the tear seam visible, especially in bright light.
The second problem is due to the difference in composition of the cast skin and, the sprayed tear seam material. In top-mount applications in which the tear seam is exposed to high temperatures and intense UV radiation, the sprayed material introduced into the tear seam ages differently than the surrounding cast material and will become clearly visible over time.
For these reasons, multi-layered structures made by the aforementioned conventional method are only employed in mid mount applications where the hidden tear seam is not exposed to direct sunlight.
In order to overcome these problems, it has been proposed to form a PVC skin layer of uniform thickness, and thereafter form the structurally-weakened tear seams by laser cutting the backside of the skin. Due to the relatively small thickness of the skin, however, it is very difficult to precisely control the depth of the cut portion. Consequently, errors in laser cutting can lead to the disposal of skins as unusable scrap. In addition, the capital investment associated with obtaining and operating a laser cutting apparatus is very high.
A need therefore exists to provide a process for making a panel-like structure containing a decorative covering having an inner surface with a structurally weakened tear seam in which the tear seam is concealed from view, even after employing the covering in top mount applications which subject the covering to prolonged use and exposure to high temperatures and intense UV radiation.